Refractometers are used to determine refractivity, or a refractive index, refractometry being recognised as a standard method of chemical analysis. The refractive index is a value that is unique for any given substance, so according to the applicable standards in this field of analysis, it must be possible to clean any parts of the refractometer that come into contact with the sample easily and thoroughly.
Commercially available devices, such as the RE 40 refractometer produced by Mettler-Toledo, usually include a housing that comprises the measurement optics and the measurement cell, the cell being loaded with the sample for measurement. The measurement optics are arranged in the device in such manner that a beam of light transmitted from a radiation source can be coupled into and out of the measurement cell. The output coupled light coming from the measurement cell after interacting with the sample substance is detected using a suitable detection device. In this context, the word light is used synonymously with radiation. Typically, the refractive index n is measured on the sodium D line, that is to say at a wavelength of 589.3 nm, but other temperatures or wavelengths can also be used. The refractive index is affected by temperature, and is usually measured at 25° C. or this temperature is used as a reference therefor. Accordingly, many refractometers are equipped with a heater for warming the sample up.
The measurement cell is closed off from the outside by a lid, which is usually attached permanently to the device, and only the surface thereof can be cleaned without significant effort. Especially if the same refractometer is to be used for different sample substances, it would be advantageous if it were possible to clean the lid easily and thoroughly to avoid contaminating a sample substance with residues of old samples.
An unmet object of the prior art is thus to provide a refractometer with an improved lid unit that enables the lid unit to be cleaned quickly and easily.